Surface mounted, high pin count integrated circuit packages have been dominated by quad flat packs (QFPS) with various pin configurations, for example, leadless, J-leaded, and gull wing leaded. These packages have closely spaced leads for making electrical connections distributed along the four edges of the flat packages. These packages have become limited by being confined to the edges of the flat pack even though the pin to pin spacing is small. To address this limitation, a new package, a ball grid array (BGA) is not so confined because the electrical contact points are distributed over the entire bottom surfaces of the packages. More contact points can be located with greater spacings than with the QFPS. These contacts are solder balls which facilitate flow soldering of the packages onto a printed circuit board. BGA's are popular alternatives to QFP's.
Sockets that accept BGA's are necessary for testing, burn-in, re-programming, and sometimes for production use where the integrated circuit may need replacing. Several such sockets have been developed by various manufacturers to satisfy this need. Most of these sockets are of a clam shell design, where a hinged top opens to allow package entry, and closing the top retains the package within the socket. The socket includes a bed of contacts spaced to match the BGA contacts and a spring load is arranged to press the package onto the bed of contacts to ensure electrical connections. Some of the prior art BGA sockets align the IC contacts in holes in a printed circuit board. The contacts are arranged to extend through the holes to the other side of the printed circuit board where electrical connections are made. Such an arrangement of enclosing the contacts within the holes has the undesirable feature of retaining heat in the BGA packages during test or bum-in. Other such sockets also enclose the these IC packages so that heat is not easily extracted.
Such prior art sockets may be adequate for small scale handling of BGA but, because of the many separate and complex physical actions needed to insert, test, and extract the BGA package, such clam shell sockets are costly, unwieldy, and unreliable when used for production processing large numbers of BGA packages.
Another limitation of available BGA sockets occurs since the socket contacts place forces onto the IC contacts in the same direction. This force drives one side of the package against an abutment of the socket. With a large number of contacts this cumulative force of many spring loaded contacts is very large and may physically damage the package.
It is an object of the present invention to provide a BGA socket needing few and simple physical operations to insert and extract an IC package. A related object is to provide a BGA socket where the ball contacts themselves enlarge the opening into the BGA socket where the construction of the socket electrical contact and the construction of the through holes retain the ball contact but allow extraction with minimal force.
It is another object of the present invention to provide a socket which balances the forces of the electrical contacts on the BGA contacts and package.
It is yet another object of the present invention to provide a BGA socket with no obstructions that need to be avoided when inserting and extracting the BGA package.
It is another object to provide a BGA socket with superior heat dissipation.